The geographical location of a User Equipment (UE) is basically calculated by measuring the delay time of signals transmitted from a plurality of cells. Accordingly, in order to measure the location of the UE, at least three signals are required. Based thereon, various methods of calculating the location of the UE exist but, in general, an Observed Time Difference Of Arrival (OTDOA) scheme is mainly used.
FIG. 1 is a conceptual diagram illustrating an OTDOA scheme for measuring a UE location.
Referring to FIG. 1, the OTDOA scheme is for measuring, by a UE, the location of the UE based on a difference in times at which signals transmitted from respective cells reach the UE, and the UE measures delay times of the signals received from the respective cells and reports the measured delay time to a serving cell or an anchor cell, and the serving cell measures the location of the corresponding UE based on the reported delay times.
In this case, various reference signals for a location-based service may be used for the signals transmitted to the UE from the respective cells. For example, a Positioning Reference Signal (PRS) may be used.
In this case, the UE may use PRSs received from the respective cells and determine the location based on an arrival time difference between the received PRSs. Alternatively, the UE may transmit information on the arrival time difference between the PRSs to the serving cell or the anchor cell, and thus the serving cell or the anchor cell may determine the location of the UE.
Meanwhile, in receiving the PRSs received from a plurality of cells, which are used for determining the location, the UE may need to distinguish PRSs of respective cells. Further, the PRSs transmitted from the respective cells are required to minimize interference of adjacent cells. That is, PRSs transmitted from cells having different cell IDs should have the low side lobe of auto correlation.
To this end, with respect to PRSs of adjacent cells transmitted for determining the location of one UE, it is required to set time-frequency patterns differently. However, the number of time-frequency patterns for the PRSs is limited by a communication system, and thus it is difficult to generate a large number of time-frequency patterns having excellent correlation attributes. That is, when a large number of PRS patterns is configured and used with limited resources, redundant Resource Elements (REs) between various patterns are overlappingly used, so that a large number of “hits” exists.
Meanwhile, according to the development of services based on a disaster situation and an accurate location of a user, a technology for accurately measuring the location of a user UE is needed. Further, many Base Station (BS) infrastructure elements such as small cells for providing a communication service in an environment in which users are concentrated are constructed.
In such a situation, research on various PRS patterns or PRS expansion for minimizing interference has been conducted according to an increase in the number of adjacent cells.